The goal of the proposed research is to develop novel fluorescence techniques and use them in concert with other experimental approaches to elucidate the structure and dynamics of selected receptor proteins. We plan to carry out the following studies: (1) We will continue our x-ray crystallographic studies of the transmembrane channel formed by gramicidin A, a peptide antibiotic, and of its complexes with alkali cations. Heavy atom derivatives will be synthesized to solve these structures at high resolution. (2) Neutron diffraction studies of the gramicidin channel are also in progress. Deuterium analogs are being synthesized to deduce the phases and the location of solvent molecules will be ascertained. (3) A new fluorescence energy transfer approach using long lifetime donors such as chelates of terbium will be applied to obtain information about lateral diffusion, lateral proximity, and transverse proximity in membranes. Changes in accessibility of chromophores can also be monitored by this technique. (4) We will use a synchronously pumped dye laser for subnanosecond studies of rotational motions of chromophores in relation to the conformational flexibility and folding of receptor proteins. In particular, the segmental flexibility of monoclonal immunoglobulins will be investigated. We are developing a subnanosecond fluorescence microscope to measure the dynamics of membrane-bound immunoglobulins. (5) We are cloning immunoglobulin genes for future sequence studies that will complement the spectroscopic experiments.